1. Field of the Invention
The invention generally relates to non-tracking solar energy collector systems and more particularly to a collector system characterized by an improved solar energy concentrator characterized by a plurality of independently supported asymmetric reflector modules for directing incident beams of solar energy on elongated strip-like segments of a flat-plate receiver arranged in mutually spaced parallelism.
2. Description of the Prior Art
Currently, substantial quantities of time and funds are being devoted to a search for sources of energy which can be utilized economically and efficiently in order that dependence on more conventional sources of energy, such as fossil fuels, may be reduced.
It has long been recognized that the sun provides a substantially endless source of solar energy. For example, it has long been appreciated that solar energy may be collected and stored in forms such as heat. Moreover, systems employed in collecting solar energy are considered to be simple and economic, both in terms of fabrication and maintenance. These recognized advantages have led many investigators toward further development of solar energy collector systems having enhanced capabilities for collecting solar energy and converting the collected solar energy to usable forms of energy.
The future success of solar energy collector systems is believed by many to be dependent in large measure upon the availability of low-cost, efficient collector systems. Vacuum insulated tube-type collectors are disclosed in U.S. Pat. No. 4,091,798. While vacuum insulated tube-type collectors which minimize thermal losses have been employed with success, high costs impair their use for domestic purposes, such as heating, absorption, refigeration and the like.
Moreover, collector systems for domestic uses must be reliable in their performance, require little maintenance, be relatively economic to fabricate, operate and maintain, and, finally, they must be characterized by high strength-to-weight ratios which facilitate a mounting thereof in domestic use environments, such as on roofs of homes and the like.
Consequently, attempts continuously are being made to improve fixed collectors and/or to reduce the costs thereof. Since non-tracking, flat-plate collectors do not require tracking or tilting, they may be said to represent the lowest capital cost per square foot of collector surface available for conversion of solar energy. The performance, unfortunately, of currently available flat-plate collectors tends to be relatively poor at elevated temperatures due to excessive heat loss from the absorber plates employed.
Among the various approaches taken in reducing radiation losses from absorber plates of flat-plate collectors is to reduce the heat loss coefficient. This has been achieved primarily by use of multiple of glazings and selective absorbers. Multiple glazings are useful but tend to reduce total transmissivity as well as increase costs. It is known that convection losses, on the other hand, can be suppressed by using honeycomb suppressors or by providing evacuated chambers between the absorber plate and a transparent cover normally provided therefor.
Unfortunately, the use of honeycomb cells tends to reduce the incoming flux by absorption and, also, increases the backward conduction. Moreover, there are potential problems inherent in plastic honeycomb materials and, of course, glass honeycombs are excessively expensive.
Reduction of convective losses through a use of evacuated chambers requires the use of good seals in order to maintain the required levels of vacuum during the lifetime of the system within which the seals are employed. Such seals are, of course, often difficult to maintain. Furthermore, it should be appreciated that for flat-plate collectors of customary dimensions, a transparent cover must be supported by suitable members, referred to as pegs, in order to eliminate stress-induced cracking resulting from forces occurring due to atmospheric pressures. These pegs, unfortunately, also tend to increase conduction losses. Furthermore, even though plastic covers offer some advantages over glass, from a stress standpoint, operational problems such as scratching, distortion and even melting under static conditions and degassing under vacuum are encountered.
Recently, evacuated tube collectors using borosilicate glass tubes have been suggested for use in non-tracking solar heat collector systems. Moreover, glass-to-metal vacuum seals apparently capable of being employed over long periods of time, without experiencing undesirable degradation, have been employed with these tube collectors. As a consequence, vacuum tubes tend to present a number of advantages over conventional flat-plate designs, from both a thermal performance and a longevity viewpoint. Unfortunately, however, when employed in non-tracking flat-plate systems, the economic costs of vacuum tubes are substantially greater than those of conventional flat-plate systems and thus render the resulting energy excessively expensive, which cannot be justified for domestic purposes.
Since no existing systems has provided a practical solution to the problem of providing for satisfactory cost effectiveness in systems capable of converting solar energy to more usable energy forms, in practical quantities, there currently exists a need for a non-tracking solar energy system which is simple and economic to fabricate, substantially efficient in operation and characterized by low initial and operational costs.